//
// Created by Yemao Luo on 2021/9/7.
//

#include <stdio.h>

int main() {
    int grade;
    scanf("%d", &grade);
    if (grade > 90) {
        printf("A");
    } else if (grade > 80) {
        printf("B");
    } else if (grade > 70) {
        printf("C");
    } else if (grade > 60) {
        printf("D");
    } else if (grade > 50) {
        printf("E");
    } else {
        printf("F");
    }
    return 0;
}

